indentation study of honeycomb sandwich composite

INDENTATION STUDY OF HONEYCOMB SANDWICH COMPOSITE

MATERIALS

AMIR FOROUTAN

A thesis submitted in fulfilment of the

requirements for the award of the degree of

Master of Engineering (Mechanical)

Faculty of Mechanical Engineering

Universiti Teknologi Malaysia

JUNE 2013

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To my beloved father, mother and my entire family member.

iv

ACKNOWLEDGMENTS

First of all, I would like to thank to ALLAH Subhanahuwataala for his bless

and his permission to giving me strength, spirit and time to complete this project and

this report. In particular, I wish to grab this opportunity to express my sincere

appreciation to my supervisor, DR. Yob Saied Bin Esmail for their advice, guidance

and encouragement that have led to the success of this project. In the process of

carrying out this project, commencing from the title deciding until the completion of

project, I was in contact with many people such as academicians, postgraduate

researchers and lab assistants. They have rendered their assistant in various aspects

and contributed towards my understanding and thoughts.

I am also indebted to Universiti Teknologi Malaysia for providing me the

facilities to carry out my project. Librarians at UTM also deserve special thanks for

their assistance in the process of my project information obtaining. My fellow friends

should also be recognized for their continual support and encouragement. My sincere

appreciation also extends to my entire course mate and others who have provided

assistance at various occasions. Their views and tips are useful indeed.

Unfortunately, it is not possible to list all of them in this limited space. Gratefully, I

have my family to support and encourage me especially, my father, my mother and

all of my family members. Thanks a lot to you all.

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ABSTRACT

This study was conducted to quasi-static indentation study of composite

sandwich panels made of glass/vinylester facesheets and polypropylene honeycomb

core. Composite sandwich panel with different material types including chopped strand

mat and plain woven glass/vinylester were analyzed numerically and experimentally.

The effects of different parameters such as types of material, number of layers of

facesheets and consequently the thickness of facesheets and the loading rate on

indentation behavior were studied numerically and experimentally and the obtained

results were compared together. The results of the research study showed that the

maximum applied load on composite sandwich panel made of plain woven

glass/vinylester and energy absorption properties is higher than chopped strand mat

glass/vinylester. Also, the results of experimental tests showed that loading rate have big

effect on load-deflection and energy absorption properties of composite sandwich panel

and by increasing the loading rate, the maximum applied load and energy absorption

properties of sandwich panel with honeycomb core is increased and there is direct

relation between the loading rate and the indentation properties of sandwich panel. The

results of finite element analysis and experimental tests were compared together and it

has found that there is difference between the obtained results.

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ABSTRAK

Kajian ini melibatkan ujikaji kuasi statik lekukan bagi plat sandwich diperbuat

dari gentian kaca/poliester kulit permukaan dan teras polipropina. Panel komposit

sandwich yang di perbuat dari bahan yang berlainan terdiri dari jenis gentian kaca

bersulam dan rawak dianalisa secara ujikaji dan kajian berangka. Kesan dari beberapa

angkubah seperti jenis bahan, ketebalan, kulit permukaan dn kadar kelajuan beban bagi

kelakuan lekukan di analisa secara ujikaji dan berangka dan keputusan yang di perolehi

di buat perbandingan. Daripada keputusan yang diperolehi dari ujian, di dadapati beban

maksimum dan tenaga serapan yang maksimum di perolehi dari permukaan kulit yang

di perbuat dari gentian kaca jenis sulam. Dari keputusan ujikaji di dapati kadar kelajuan

beban juga mempengaruhi kadar serapan tenaga, dimana apabila kadar kelajuan beban

bertambah akan meningkatkan kadar serapan tenaga sebelum panel tersebut gagal.

Keputusan yang diperolehi menunjukkan ada pertalian yang rapat diantara kadar

kelajuan beban dan sifat bahan sandwich dari segi ujian lekukan. Keputusan dari ujikaji

juga dibuat perbandingan dengan kaedah berangka.

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TABLE OF CONTENT

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF SYMBOLS xvii

1 INTRODUCTION 1

1.1 Background 1

1.2 Introduction 4

1.3 Scope of study 4

1.4 Statement of problems 5

1.5 Layout of thesis 6

2 LITERATURE REVIEWS 7

2.1 Introduction 7

2.2 History of the composite materials 7

2.2.1 Fibres in composite material 8

2.2.2 Matrixes in composite material 10

2.3 Sandwich panels and core materials 12

2.3.1 Sandwich Panels 13

2.3.2 Core materials 13

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2.4 Manufacturing process 16

2.4.1 Hand layup 16

2.4.2 Vacuum bagging process 16

2.4.3 Autoclave 18

2.4.4 Filament winding process 18

2.5 Composite sandwich panel subject to different

types of loading 19

2.6 Conclusion 23

3 Methodology 24

3.1 Introduction 24

3.2 Experimental procedure 24

3.2.1 Sample preparing 25

3.2.2 Indentation test 36

3.2.3 Failure analysis after indentation test 38

3.3 Finite Element Analysis 39

3.3.1 Structural finite element analysis 42

3.3.2 Engineering data 44

3.3.3 Modeling 46

3.3.4 Meshing 47

3.3.5 Applying boundary conditions and loads 48

3.3.6 Solving 49

4 RESULTS AND DISCUSSION 51

4.1 Introduction 51

4.2 Finite Element Modeling 51

4.2.1 Source of errors 52

4.2.2 Model verification and analysis parameters 53

4.3 Deformation behaviour of sandwich panel subject

to indentation loading 56

4.4 Effect of type of materials of facesheets on

Deformation behaviour of sandwich panel subject


4.5 Total energy absorption behaviour of sandwich

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panel subject to indentation loading 67

4.6 Finite element stress and deformation behaviour of

sandwich panel subject to indentation loading 71

5 CONCLUSIONS 84

5.1 Overall Conclusions 84

5.2 Recommendation 86

5.3 Determination of laminate properties 80

5.4 Failure test of general composite dome Ends

Subject to internal pressure 84

5.5 Conclusion 89

REFERENCES 87

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LIST OF TABLES

TABLE NO. TITLE PAGE

1.1 A comparison of representative material properties 2

3.1 The configuration of specimens for indentation tests 35

3.2 Material properties of plain woven glass/vinylester 45

3.3 Material properties of chopped strand mat glass/vinylester 45

3.4 Material properties of polypropylene honeycomb core 45

4.1 The experimental results of composite sandwich panel subject

to indentation loading with loading rate of 4mm/min 60

4.2 The value of maximum applied load on sandwich panel in

finite element modeling 72

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 The schematic of composite sandwich panel. 3

1.2 Three types of honeycomb core materials 3

2.1 Typical Honeycomb Sections 14

2.2 Schematic of hand layup process 17

2.3 The schematic of vacuum bagging process. 17

2.4 Filament winding process. 19

3.1 Cleaning the prepared mold (glass) by using acetone liquid 25

3.2 Two types of mold release agent 26

3.3 Applying mold release agent on the surface of glass. 26

3.4 Preparing resin and glass fibre for fabrication 27

3.5 Saturating the fibres with resin by using brush and roller 27

3.6 Applying a layer of core over the laminate 28

3.7 Fabrication of second facesheet of sandwich panel 28

3.8 Fabrication of second facesheet of sandwich panel 29

3.9 Applying a layer of perforated film 29

3.10 Applying a layer of absorber 30

3.11 Tubing system in vacuum bagging process 30

3.12 Applying a layer of bagging film over the laminate 31

3.13 Covering the system with bagging film and sealant tape 31

3.14 Connecting the system to resin collector 32

3.15 Absorbing the excess resin by absorber under

vacuum pressure 32

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3.16 Curing process of laminate under vacuum pressure 33

3.17 Vacuum bagging process of composite sandwich panel 34

3.18 Band saw machine for cutting the samples for

indentation tests 34

3.19 The prepared sample for indentation test 35

3.20 The test rig for indentation tests of composite

sandwich panel 36

3.21 Load-Deflection curve of sandwich panel subject to

indentation loading 37

3.22 Failure analysis of composite sandwich panel subject


3.23 Three types of finite elements 40

3.24 Modeling of composite sandwich panel subject to

indentation loading by using ANSYS Software (Front view) 46

3.25 Modeling of composite sandwich panel subject to

indentation loading by using ANSYS Software (Side view) 46

3.26 The meshing of composite sandwich panel subject to


3.27 The applied load over the indentor in finite element analysis 48

3.28 The boundary condition in finite element analysis of

sandwich panel 48

3.29 The deformation behaviour of sandwich panel subject to


3.30 The deformation behaviour of sandwich panel subject to

indentation loading with hidden top facesheet 49

3.31 The stress behaviour of sandwich panel subject to


4.1 The effects of number of elements on total deformation of

composite sandwich panel subject to indentation loading 54

4.2 Finite element model of sandwich panel with optimum

number of elements 54

4.3 The comparison between the results of experimental tests

and finite element analysis 55

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4.4 Load –deflection behaviour of sandwich panel made of two

layers of chopped strand mat glass/vinylester facesheets 57

4.5 Load –deflection behaviour of sandwich panel made of three


4.6 Load –deflection behaviour of sandwich panel made of four


4.7 Load –deflection behaviour of sandwich panel made of

two layers of woven glass/vinylester facesheets 58

4.8 Load – deflection behaviour of sandwich panel made of

three layers of woven glass/vinylester facesheets 59

4.9 Load – deflection behaviour of sandwich panel made of

four layers of woven glass/vinylester facesheets 59

4.10 Load – deflection behaviour of sandwich panel made of two

layers of plain woven and chopped strand mat glass/vinylester

facesheets subject to indentation loading with loading

rate 4mm/min 61

4.11 Load – deflection behaviour of sandwich panel made of three



rate 4mm/min 62

4.12 Load – deflection behaviour of sandwich panel made of four



rate 4mm/min 62




rate 6mm/min 63




rate 6mm/min 63

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rate 6mm/min 64




rate 8mm/min 65




rate 8mm/min 65




rate 8mm/min 66

4.19 Energy absorption of sandwich panel made of two layers of

chopped strand mat glass/vinylester subject to indentation

loading with different loading rate 68

4.20 Energy absorption of sandwich panel made of three layers of



4.21 Energy absorption of sandwich panel made of four layers of



4.22 Energy absorption of sandwich panel made of two layers

of plain woven glass/vinylester subject to indentation loading

with different loading rate 69

4.23 Energy absorption of sandwich panel made of three layers



4.24 Energy absorption of sandwich panel made of four layers


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4.25 finite element stress analysis of sandwich panel made of two

layers of plain woven glass/vinylester subject to 1556N


4.26 Finite element deformation analysis of sandwich panel made

of two layers of plain woven glass/vinylester subject to 1556N


4.27 Finite element stress analysis of sandwich panel made of three



4.28 finite element deformation analysis of sandwich panel made

of three layers of plain woven glass/vinylester subject to

1928N indentation loading 74

4.29 Finite element stress analysis of sandwich panel made of four




of four layers of plain woven glass/vinylester subject to 2290N


4.31 Finite element stress analysis of sandwich panel made of two

layers of chopped strand mat glass/vinylester subject to 772N


4.32 Finite element deformation analysis of sandwich panel

made of two layers of chopped strand mat

glass/vinylester subject to 772N indentation loading 78

4.33 Finite element stress analysis of sandwich panel made of

three layers of chopped strand mat glass/vinylester

subject to 966N indentation loading 79


of three layers of chopped strand mat glass/vinylester subject

to 966N indentation loading 79

4.35 Finite element stress analysis of sandwich panel made of

four layers of chopped strand mat glass/vinylester subject

to 1383N indentation loading 81

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4.36 Finite element deformation analysis of sandwich panel

made of four layers of chopped strand mat

glass/vinylester subject to 1383N indentation loading 81

4.37 The comparison between the results of finite element stress

analysis of sandwich panel made of different number of

chopped strand mat and woven facesheet 82

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LIST OF SYMBOLS

t - The thickness of facesheets

E - Energy absorption

F - Load

- Deflection of sandwich panel

E - Modulus elasticity

v - Poison ratio

G - Shear modulus

- Stress

CHAPTER 1

INTRODUCTION

1.1 Background

Composite materials are composed of reinforcements such as fibres,

particles, and flakes that surrounded in a matrix (resin) such as polyester, epoxy, and

vinylester. The resin holds the fibres together to create products with any shape and

transfer the applied load to the fibres and the fibres improve the physical and

mechanical properties of the resin and most of the applied loads are taken by the

fibres. Fibre reinforced polymer materials unlike common materials such as steel and

aluminum are not isotropic materials and they are anisotropic. The mechanical

properties of anisotropic materials are not same in any direction and the mechanical

properties are different in different directions while the mechanical properties are

same in any direction in isotropic materials. Therefore, fibre reinforced polymers are

directional materials or in other words, the optimum mechanical properties are in

direction of reinforcement. Therefore, the fibres are placed in the composite

materials according to the applied load. Also, the type and direction of

reinforcements are selected according to the application.

Fibre reinforced polymer materials have been used in a wide range of

applications, the primary focus of which involves either mass reduction or resistance

to corrosive environments. Consequently the aerospace, motor sport and boating

industries have dominated FRP usage. These would indicate that FRPs possess

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substantial potential for the production of structures which are not only low in mass,

but are practical, cost competitive alternatives to more traditional materials.

A comparison of materials properties of common materials such as aluminum

and steel and composite materials such as carbon/epoxy and E-glass/epoxy were

listed in Table 1. It can be seen from Table 1.1 that the composite materials provide

several advantages such as high stiffness to weight ratio over the common materials.

Although the fibre reinforced polymer materials have several advantages, but the

cost of this materials are the disadvantages of composite materials.

Table 1.1: A comparison of representative material properties

Type of

materials

Density

(kg/m3)

Tensile

Strength

(MPa)

Tensile

Modulus

(GPa)

Max.

Elastic

(%)

Specific

Tensile

Strength (Ult.)

(MPa/kg/m³)

Specific

Tensile

Modulus

(Mpa/kg/m³)

Carbon/Epoxy 1750 1000(UTS) 100 1.0 0.57 57

E-glass/Epoxy 2540 700 (UTS) 40 1.75 0.28 16

Steel 7850 350 (Yield)

480 (UTS)

200 0.18 0.06 25

Aluminium 2800 110 (Yield)

151 (UTS)

69 016 0.05 25

Composite sandwich materials are special types of composite materials that

are manufactured by bonding two skins (Facesheet) to a core (Figure 1.1). The

facesheets are very thin and stiffness of them is very high and the core materials

usually are light and thick in comparison with the facesheets. Any type of materials

such as aluminum, steel, carbon/epoxy and glass/vinylester can be used as facesheets

the materials such as aluminum honeycomb, Polypropylene honeycomb, foam core

can be used as core materials in sandwich panels and this materials usually have low

strength and low weight materials, but higher thickness of these materials provide the

sandwich composite materials with high bending stiffness with low weight.

3

Figure 1.1 The schematic of composite sandwich panel.

The structures that naturally have the geometry of honeycomb shape are

known as honeycomb structures. The minimum amount of materials is used in

honeycomb materials. Therefore, the cost of raw materials in honeycomb materials is

very low but the manufacturing process has a high effect on the cost of these

materials. Different types of materials such as paper, aluminum, steel, composite

materials and plastic can be used in fabrication of honeycomb materials. Aluminum

honeycomb, polypropylene honeycomb and paper honeycomb are three examples of

honeycomb materials (Figure 1.2).

(a) Aluminum honeycomb (b) paper honeycomb (c) polypropylene honeycomb

Figure 1.2 Three types of honeycomb core materials.

4

Polypropylene honeycomb material is one of the widely used honeycomb

materials that are used in composite sandwich panel. This material is made of

polypropylene materials. In this material, the ratio of strength to weight is high and

the resistance to chemical and corrosion and energy absorption property is very high

and thermoforming ability and recyclable is two other advantages of this material.

1.2 Introduction

This study deals with experimental and numerical investigations of composite

sandwich panel with polypropylene honeycomb core and different number of layers

of chopped strand mat and woven glass/vinylester including two, three and four

layers under quasi static indentation loading. Experimental tests were conducted on

composite sandwich panel subject to indentation loading with different loading rate

including 4mm/min, 6mm/min and 8mm/min by using Instron universal testing

machine. All of the specimens for experimental testing were fabricated by using

vacuum bagging process. For different types of sandwich panels with polypropylene

honeycomb core, the contact force-displacement curves and energy absorption-

displacement curves of composite sandwich panel were determined and analyzed and

the obtained results were compared together.

Also, the numerical investigation of composite sandwich panels was

studied by using ANSYS Workbench Software. In this section, static analysis of

composite sandwich panels with polypropylene honeycomb core subject to

indentation loading were modeled and studied and the deformation behaviour and

stress behaviour of sandwich panels were determined and compared with the

results of experimental tests.

1.3 Scope of study

The scopes of this research are listed below:

5

Literature study on composite material and composite sandwich material

subject to different types of loading including indentation loading.

Preparation of different forms of composite sandwich materials with

polypropylene honeycomb core and different number of layers of

chopped strand mat and woven glass/vinylester facesheets by using

vacuum bagging process.

Perform experimental quasi-static indentation tests on composite

sandwich panel and data collecting.

Calculating the contact force-displacement curves and energy absorption-

displacement curves of composite sandwich panel at different loading

rate.

Finding the effect of different parameters such as the number of layers

and type of facesheets and the loading rate on indentation properties of

composite sandwich panel.

Finite element analysis of composite sandwich panel with polypropylene

honeycomb core subject to indentation loading.

Comparing the results of finite element analysis with the experimental

and validate.

Defining the stress and deformation behaviour of composite sandwich

panel subject to indentation loading numerically.

1.4 Statement of problems

Composite sandwich panels are made of two facesheets and core material.

The type of facesheets and core material and the geometry of sandwich panel are

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most important factors in designing of sandwich panel. Therefore, understanding the

effect of these parameters such as the thickness of facesheets and type of materials of

facesheets on mechanical behaviour of these structures is important in design and

analyze of these structures. Therefore, In this research, the effect of different

parameters such as the type of materials including chopped strand mat and woven

glass/vinylester and the loading rate on mechanical properties of sandwich panel with

polypropylene honeycomb core especially indentation properties were studied

experimentally and numerically and the force-displacement curve and energy

absorption-displacement curve were determined.

1.5 Layout of thesis

This thesis is consist of six chapters; Introduction, Literature review, finite

element analysis, Experimental procedure, Results and discussion and Conclusions

and recommendation. Chapter 1 defines composite materials and composite

sandwich panels, introduction, state of problems, objective and scope of the study. In

Chapter 2, history of composite materials and literature reviews on the subject of

composite sandwich panel and different types of loading on these types of materials.

In Chapter 3, finite element analysis of composite sandwich panels subject to

indentation loading was presented. In Chapter 4 the experimental procedure of

composite sandwich panels with polypropylene honeycomb core was defined. In

Chapter 5, the results of experimental tests and finite element analysis were

described and the effects of different parameter on indentation properties of

composite sandwich panel were studied and the experimental results and numerical

results were compared together. In Chapter 6, Conclusions were drawn from the

experimental and numerical results and then recommendation was presented.

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indentation study of honeycomb sandwich composite

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